import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long sumOfGroup(int k) {
        int n = k-1;
        int numtobeignored = (n*(n+1) )/2;
       // System.out.println(numtobeignored);
        int sum =0;
        int j = numtobeignored +1;
        for(int  i = 1 ;i <= k;i++) {
           // System.out.println(j);
            sum += ((j*2) -1);
            j++;
        }
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}